Process for production of photographic silver halide emulsions



United States Patent 5 Claims. (in. 96-114) The present invention is directed to the production of silver halide emulsions for photographic purposes and more particularly to an improved method for the flocculation step ofthe silver halide in the making of the photographic composition.

It has been known for a long time to flocculate photographic silver halide emulsions, either in order to concentrate the silver halide or in order to circumvent the cumbersome solidification and washing process, by suitable means and to disperse them again in a desirable amount of gelatin solution and then to subject them to a photographic aging process. Such known flocculating agents are, for instance, sulfates of the alkali or alkaline earth metals which, added in large amount to the photo graphic emulsions, eliminate the protective action of the gelatine for silver halide, both in the acid and in the alkaline pH range, by removing water from the gelatine micelles.

One disadvantage of this method is that in the case of the precipitated silver halide, upon the decantation with water which is necessary for the purification, a dispersing immediately sets in again due to the absorption of water by the gelatin micelles so that large losses of silver halide must be expected. Other flocculating agents are for instance gelatine derivatives, i.e. gelatines which have, for instance, been benzylated on an amino group. The emulsions prepared with these derivatives are flocculatable, as for instance, in case of the use of anionic soaps as flocculating agents only in acid pH ranges, about 3.5,

where a disturbance of the sensitivity of the photographic emulsion is already noted.

The invention is intended and adapted to overcome the difliculties and disadvantages inherent in the production of photographic compositions of the silver halide type, it being among the objects thereof to provide a process in which the use of large quantities of sulfates is avoided and in particular wherein such use of sulfates may be eliminated.

It is also among the objects of the invention to provide a process of the type described wherein flocculation in the alkaline range of pH may be readily obtained.

It is further among the objects of the invention to introduce into the flocculation the use of compounds having at least one sulfonic radical, whereby improved results are obtained.

In the practice of the present invention the method of producing photographic silver halide emulsions is characterized by the fact that for the flocculation, copolymers of vinyl pyridine sulfonic acid or vinyl pyridine disulfonic acid with a monomeric substance such as acrylic acid, styrene sulfonic acid or the like are used. These flocculating agents, without the use of any or with the use of only a fraction of the previously customary amounts of alkali or alkaline earth metal sulfates, effect the flocculation of silver halide emulsions in weakly acid, in neutral and particularly in the alkaline pH range and thereupon a dependable washing by decantation with water takes place without redispersing of the silver halide occurring. The new flocculating agents are copolymers of vinyl pyridine sulfonic acid or vinyl pyridine disulfonic acid with any monomeric substance capable of polymerizing. The decisive factor in connection with these products is the introduction of the sulfonic acid radical or the disulfonic acid radical onto-vinyl pyridine since it has been found that only thereby does flocculation in the alkayine pH range become possible;

The monomers which are copolymerized are as follows:

Acrylic acid -Acrylic acid-I-acrylate Acrylic acid-i-acrylonitrile Acrylic acid+styrene sulfonic acid Methacrylic acid Acrylic acid ester Methacrylic acid ester Methylchloracrylic acid ester Acrylonitrile Methacrylonitrile Acrylamide Styrene sulfonic acid Divinyl benzene sulfonic acid The following are specific examples of the operation of this invention:

Example 1 A mixture of 3 ml. of 4-vinyl pyridine in 27 ml. of acrylic acid is introduced into a solution of 0.15 gram of K S O in 60 cc. of water at 50 C. and polymerized in the customary manner. The anhydrous copolymer is thereupon sulfated with concentrated sulfuric acid and 100 mg. of cadmium chloride at 120 C. forabout one hour. Thereupon, it is neutralized to a pH of 8 with sodium hydroxide solution and the sodium sulfate is removed by crystallization; The 2% aqueous solution of the copolymer of acrylic acid and vinyl pyridine sul- Emulsifying.At the 0, 10th and 20th minutes, separate portions of cc. of Solution H are introduced into I, whereupon the emulsion is cooled to 30 C. and brought to a pH of 8.5 by means of 25% sulfuric acid. The flocculation is eflected by the addition of 70 cc. of the 2% solution of the above described copolymer. The supernatant solution can now be poured off and the product washed with water as many times as desired. The flocculate is thereupon dispersed in a solution of 35 grams of gelatine in 600 cc. of water and aged until optimum sensitivity is obtained.

Example 2 A mixture of 28.5 grams of styrene and 1.5 grams of vinyl pyridine is introduced at 60 C. into a solution of 60 cc. of water, 0.3 gram of lauryl sulfate, 0.03 gram of sodium phosphate and 0.5 gram of K S O and polymerized by further heating. The dry copolymer is then sulfated with concentrated sulfuric acid and mg. of cadmium chloride for 1 hour at C., and then dissolved in water. Thereupon it is brought to a pH of 8, by means of sodium hydroxide solution. The resultant sodium sulfate is preferably allowed to crystallize out of the concentrated solution which is then diluted so that there is present an approximately 2% solution of the copolymer. The fiocculating agent thus obtained can be used in the following boiling emulsion.

SolutionI:

H O 1 250.0 Gelatine 1 5.0 KBr 1 32.0 KI 1 1.8

Solution II:

AgNO 2 40.0 H O to make up to 2 300.00

Emulsifying.-At the 0, 10th and 20th minutes, separate portions of 100 cc. of Solution II are introduced into I. For the flocculation '40 cc. of the above 2% copolymer solution are then added. After the settling of the flocculate, the supernatant liquid is poured OE, and the flocculate can be washed as many times as desired. Thereupon the silver halide is dispersed in a solution of 60 grams of gelatine in 750 cc. of water and aged until optimum sensitivity is obtained.

Example 3 The copolymer of styrene sulfonic acid and vinyl pyridine sulfonic acid described in Example 2 can also be used .in the following ammonia emulsion, in which within a pH range of 11-12, the flocculation is supported by sodium sulfate and there is produced a readily washable flocculate.

Emulsifying- -At the 0, 10th and 20th minute, separate portions of 80 cc. each of Solution II" are added to I, whereupon the emulsion is cooled to 30 C. cc. of the aforementioned 2% solution of the copolymer is now added, and the emulsion is then flocculated with a solution of 25 grams of sodium sulfate in 80 cc. of water. After the pouring off, Washing can be effected as many times as desired, and the flocculate can then be dispersed in a solution of 35 grams of gelatine and 600 cc. of water. The emulsion can now be aged as customary until optimum sensitivity is obtained.

We claim:

1. Process for the production of photographic silver halide emulsions which comprises providing a gelatine emulsion of silver halide, in Water, mixing said emulsion with the sulfonated copolymer of vinyl pyridine and a polymerizable monomer selected from the class consisting of acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, styrene sulfonic acid, divinyl benzene sulfonic acid, and acrylamide, and flocculating said emulsion in alkaline medium to form a silver halide flocculate, separating said fiocculate from the reaction mixture, and then dispersing said fiocculate in a gelatine solution.

2. Process according to claim 1 characterized in that there is introduced an additional fiocculating agent taken from the class consisting of the alkali and alkaline earth metal sulfates.

3. Process according to claim 1 characterized in that the pH of the flocculating medium is alkaline.

C 4. Process according to claim 1 characterized in that the pH of the fiocculating medium is acid.

5. Process according to claim 1 characterized in that the pH of the flocculating medium is neutral.

References Cited by the Examiner UNITED STATES PATENTS 2,484,456 10/49 Lowe et al. 260-88.3 2,717,887 9/55 Saner 260-883 2,725,381 11/ Reynolds 260-4583 2,787,545 4/57 Gates et al. 96114 2,837,500 6/58 Andres et al. 260-793 3,022,172 2/ 62 Ohba et al. 96--94 NORMAN G. TORCHIN, Primary Examiner.

HAROLD N. BURSTEIN, Examiner. 

1. PROCESS FOR THE PRODUCTION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS WHICH COMPRISES PROVIDING A GELATINE EMULSION OF SILVER HALIDE, IN WATER, MIXING SAID EMULSION WITH THE SULFONATED COPOLYMER OF VINYL PYRIDINE AND A POLYMERIZABLE MONOMER SELECTED FROMTHE CLASS CONSISTING OF ACRYLIC ACID, METHACRYLIC ACID, ACRYLONITRILE, METHACRYLONITRILE, STYRENE SULFONIC ACID, DIVINYL BENZENE SULFONIC ACID, AND ACRYLAMIDE, AND FLOCCULATILNG SAID EMULSION IN ALKALINE MEDIUM TO FORM A SILVER HALIDE FLOCCULATE, SEPARATING SAID FLOCCULATE FROM THE REACTION MIXTURE, AND THEN DISPERSING SAID FLOCCULATE ILN A GELATINE SOLUTION. 